There is a global urgency to develop a protective vaccine against HIV-1. Neutralizing antibodies (Nabs) can provide effective prophylaxis against HIV-1 infections. However, eliciting Nabs that are broadly reactive against many antigenically diverse HIV-1 isolates has been a major challenge and it remains a critical roadblock to HIV-1 vaccine development. The primary objective of the studies being proposed is to generate novel antigens that are able to elicit broadly reactive Nabs on the mucosal surface, with a long-term goal of developing a vaccine against the virus. Specifically, we propose to target the membrane-proximal external region (MPER) of gp41 by generating recombinant lactic acid bacteria (LAB) that express antigenically intact gp41 protein fragments on the cell surface using a novel technology. The scope of this proposal is limited to the following specific aims: (1) to generate recombinant Lactobacillus casei that display HIV-1 gp41 MPER on the cell surface, (2) to devise an optimal vaccine strategy and to evaluate immunogenic properties of recombinant L. casei in mice, and (3) to elicit broadly reactive Nabs against HIV-1 gp41 MPER in XenoMouse. Successful completion of this study will generate novel vaccine candidates and strategies for eliciting protective humoral immune responses, which would represent a major step forward in AIDS vaccine development efforts.